The invention relates to an unwinding apparatus for a strapping machine for the purpose of unwinding a band from a band-supply reel.
Such an unwinding apparatus is used to supply the relevant strapping machine with the band material which is required therein for the purpose of strapping a respective item which is to be strapped.
In a known unwinding apparatus of the type mentioned in the introduction, a relatively small band-supply reel is clamped in between two rolling flanges which are connected to one another via a threaded shank with associated nut. The rolling flanges are located on two rollers, of which one is driven. Accordingly, at constant drive speed, the band length unwound per unit of time decreases correspondingly as the band-supply reel becomes smaller. The unwound band is fed into a box-like supply container, from which the strapping machine draws off the band. The band supply lies in an unordered fashion in the supply container, and the band which is conveyed rearward by way of the strapping machine hangs out. Side walls which are considerably lower than the rolling flanges are provided. In addition to a reduced guiding action, there is thus also a certain risk of accident since undesired contact between the rotating parts cannot be ruled out.
The object of the invention is to provide an improved unwinding apparatus of the type mentioned in the introduction, in which the abovementioned disadvantages are eliminated.
This object is achieved according to the invention by at least two bearing rollers which are located one behind the other in the rotational direction of the band-supply reel and on which the band-supply reel rests by way of its respective outer band circumference, it being possible for at least the downstream bearing roller to be driven for the purpose of driving the band-supply reel.
This design also makes it possible to use, in particular, larger band-supply reels. Since the band-supply reel rests directly on the bearing rollers by way of its respective outer band circumference, the speed of unwinding from the band-supply reel, at constant rotational speed of the drive, is always the same irrespective of the diameter of said band-supply reel. Even relatively large and heavy band-supply reels can be handled easily. The relevant reels can provide an extremely large band supply. The necessary outlay in control terms is minimal.
The downstream bearing roller is expediently provided with a rubber casing. By virtue of such a rubber casing on the downstream bearing roller, it is possible, in particular when the two bearing rollers are driven, to prevent band sections from bulging out between said two rollers. By virtue of the increased friction between the rubber casing and the band-supply reel, the downstream bearing roller has a drive-determining function. This is the case, in particular, when the upstream bearing roller has a surface made of, for example, steel, with the result that said upstream bearing roller serves predominantly for bearing purposes. It is thus also conceivable, in particular, for merely the downstream bearing roller to be driven.
The unwinding apparatus expediently comprises two fixed side walls which are preferably no less than the height as the band-supply reel and between which it is possible to introduce the band-supply reel, which is to be lowered onto the bearing rollers. The side walls give the band-supply reel the desired stability. It is also conceivable to roll the band-supply reel onto the bearing rollers between the side walls.
The side walls may be provided with recesses which are open in the upward direction and extend into the region of a central cavity of the band-supply reel, said cavity being defined, in particular, by a hollow-cylindrical core. It is thus the case that, with the band-supply reel set down, the central cavity of the latter is accessible in order for it to be possible, for example, for a carrying strap by means of which the band-supply reel was previously fastened on a crane to be removed again.
In a preferred practical embodiment, the unwinding apparatus comprises an intermediate band store via which the band unwound from the band-supply reel is fed to the strapping machine and kept taut. Since the band is always kept taut by the intermediate band store, the situation where band which is conveyed rearward by way of the strapping machine hangs out is ruled out.
The drive of the band-supply reel can expediently be activated in dependence on the respective state of the intermediate band store and/or the quantity of band material stored in the intermediate band store. It is thus possible to prevent continued unwinding of band material once the drawing-in operation of the band in the region of the strapping machine has been stopped.
It is advantageous for at least one weight lever to be provided in order to load the band-supply reel, which rests on the bearing rollers, downward in the direction of the bearing rollers. This ensures that the band-supply reel, which becomes increasingly lighter in the direction of the end of the supply, or the remaining core does not spring off from the bearing rollers. The weight lever may be mounted, for example, pivotably on the fixed side walls.
The band unwound from the band-supply reel is expediently guided generally upward to the intermediate band store.
In a preferred practical embodiment of the unwinding apparatus according to the invention, the intermediate band store, in the manner of a block and tackle, comprises at least two deflecting rollers over which the unwound band is guided, with a reserve band supply being formed in the process, there being provided at least one top deflecting roller, which is mounted in a stationary manner, and at least one bottom deflecting roller, which can be displaced in the vertical direction.
In this case, the bottom deflecting roller may be mounted, in particular, on a carriage which can be displaced in the vertical direction along, a carriage guide.
The drive of the band-supply reel can advantageously be activated depending upon the vertical position of the bottom deflecting roller or of the carriage. In this case, said drive of the band-supply reel is expediently activated such that it is switched on if the bottom deflecting roller or the carriage assumes a predeterminable position, or is located above the same, and is switched off if the bottom deflecting roller or the carriage is located beneath said predeterminable position.
For the purpose of monitoring the vertical position of the bottom deflecting roller or of the carriage, at least one sensor is expediently provided. In this case, it is possible to provide, in particular, at least one vertically adjustable sensor preferably assigned to the carriage guide.
The circumferential speed of the at least one driven bearing roller is essentially equal to the speed at which the band is drawn into the strapping machine. With the drive of the band-supply reel switched on, the situation where more band material than is required by the strapping machine is supplied is thus prevented.